Clearcoat-basecoat composite coatings are widely used in the coatings art and are notable for desirable gloss, depth of color, distinctness of image and/or special metallic effects. Composite systems are particularly utilized by the automotive industry to achieve advantageous visual effects, especially a high degree of clarity. However, a high degree of clarity in the clearcoat makes it easier to observe defects.
Clays and silicas have been included in coating compositions to act as rheology control agents. In this capacity, the clays and silicas associate after spray application to form or re-form aggregates that thicken the applied coating to prevent sagging.
Aqueous silica sols have been converted into organic sols. The conversion methods have produced less than satisfactory organosols for coatings, however, because the sols are relatively high in organic solvent, generally include a solvent that would not have been selected for the particular coating, and if used in higher amounts the organic silica sols to date have tended to flocculate in organic coatings to produce a matt or reduced gloss coating. Campbell et al. in U.S. Pat. No. 5,853,809 describe adducting onto inorganic particles of an organic sol a group that reacts with a film former of a coating composition. In this case, the inorganic sol particles can be included in higher levels without flocculation, but the problem of the costly transfer of the particles from aqueous to organic sol remains, as well as an additional cost for the modification step.
Thus, it would be desirable to improve resistance of a clearcoat coating layer to scratching and marring without incurring the high cost associated with currently available silica organosols, particularly in an organic medium, as most clearcoat compositions are organic solvent compositions.